Resuscitation, as that term is herein used, refers generally to externally exerted efforts to assist or restore breathing of a patient whose natural breathing has either become impaired or has ceased, or to at least temporarily attempt to emulate the effects of more natural breathing in the patient. Resuscitation involves forcing air or oxygen under appropriate pressure through the patient's natural airway system and into his lungs to inflate the latter at appropriate intervals separated by periods during which such application of air or oxygen under pressure is interrupted (and an external physical pressure may be applied to the patient's chest) to permit the previously applied air to escape from the patient's lungs and the latter to deflate.
The forms of previous resuscitators of greatest interest as background for this invention, commonly called "squeeze bag" or "bag-valve-mask" resuscitators, employ some type of manually compressible and self-restoring bag having the interior thereof in fluid communication with a face mask. In its most primitive conceptual form, such a device could be operated for resuscitation purposes simply by applying the mask to the face of a patient, manually squeezing the bag to force air from the bag through the mask and into the patient's lungs, releasing the squeezing pressure from the bag and removing the mask from the patient's face to permit escape of air from the patient's lungs. At the same time, the bag would restore itself and thereby self-inflate with fresh atmospheric air through the mask. The bag would then remain in its restored condition until the next bag squeezing operation and such cycle would be repeated as necessary. A squeeze bag resuscitator thus permits a trained person administering treatment to directly control both the quantity of air forced into the patients lungs and the intervals of doing so to best suit the condition of the patient through choice of the extent and timing of squeezing of the bag.
Even relatively early squeeze bag resuscitators soon incorporated various refinements, including employment of resilient squeeze bags adapted to be conveniently held in one hand with the face masks carried more or less directly on the frontal extremities of the bags to increase portability and facilitate use by a single person. A bag fill valve (an inward flow permitting check valve for communicating the interior of the bag with the atmosphere) was introduced to permit refilling of the bag with fresh air during its restoration phase without removing the mask from the face of the patient. And, in conjunction with the bag fill valve came the evolution of the patient non-rebreathing valve assembly. Such assembly is interposed between the bag and the mask and permits fresh air to move from the bag into the mask during the squeeze phase, but vents to the atmosphere air returned to the mask from the patient's lungs during the bag restoration or restored phases, thereby preventing passage of the expired air into the bag from which it would be forced back into the patients lungs or "rebreathed" during the next squeeze phase.
During the course of development of squeeze bag type resuscitators, it was recognized that it would be desirable to administer oxygen, or at least oxygen enriched air, rather than merely atmospheric air, in treating some resuscitation patients.
Accordingly, the development of practical means for introducing oxygen into the squeeze bag initially entailed providing "oxygen enrichment" for the air drawn into the squeeze bag from the atmosphere during the restoration phase of the bag cycle. A common and still prevalent approach to oxygen enrichment is to provide an elongate tube of relatively large diameter having one end thereof in fluid communication with the fill valve opening of the bag (typically at the extremity of the bag opposite from the non-rebreathing valve and mask) and the other end thereof exposed to the atmosphere, together with a considerably smaller tube extending into the larger tube and coupled with a pressurized oxygen source for continuously releasing oxygen into the air entering and accumulating within the large tube from the atmosphere. Such devices are commonly call "oxygen accumulators" and are effective to introduce a mixture of air reasonably enriched with oxygen into the bag during the restoration phase of its cycle, without significantly increasing the pressure within the bag (since one end of the large tube of the accumulator is in free communication with the atmosphere). Examples of these and other oxygen accumulator resuscitators may be found in U.S. Pat. Nos. 4,501,271, 4,774,941, 4,821,713, 5,067,487, 5,109,840, 5,140,982 and 5,279,289. A notable shortcoming of resuscitators of this sort is that the concentration of the continuously flowing oxygen gas is subject to dilution by the ambient air with which it is mixed.
In the oxygen accumulator resuscitators described in U.S. Pat. Nos. 4,821,713, 5,067,487 and 5,140,982, two discrete, sequentially operable valves are provided to deliver the air/oxygen mixture, first into the tubular member and thereafter into the face mask. Each valve possesses a comparatively high spring bias. As such, the first valve can only be opened by releasing the squeeze bag from a compressed state, and the second valve only by again squeezing the bag. In other words, the subject's spontaneous inspiratory efforts are incapable of operating the valves. This situation is exacerbated by the presence of the mask expiration port that is in direct fluid communication with the atmosphere which assures that insufficient negative inspiratory pressure can be developed in the mask to effect valve actuation.
Further, the advent of the oxygen accumulator squeeze bag resuscitator did not satisfy the need for being able to administer substantially pure oxygen to patients under certain relatively frequently occurring high oxygen demand circumstances, such as resuscitation responsive to cardiac distress or like conditions. The invention disclosed in U.S. Pat. No. 3,796,216, however, represented an early attempt to administer essentially pure oxygen to a subject using a squeeze bag resuscitator. The apparatus disclosed therein included a body member, a squeeze bag, an oxygen inlet, a flapper valve and a face mask. The body member comprises a tubular portion to which the mouth of the squeeze bag is connected. The face mask is joined to the tubular member generally opposite the squeeze bag and an inlet adapted to be connected to a source of breathing gas such as oxygen is provided in the tubular member between the squeeze bag and the face mask. The flapper valve regulates passage of oxygen from the squeeze bag to the face mask.
Unlike those discussed above, the squeeze bag disclosed in U.S. Pat. No. 3,796,216 is not self-restoring but merely flexible or pliable and is continuously inflated with oxygen via the oxygen inlet. When the bag is sufficiently inflated and it is desired to administer oxygen to the subject, the user squeezes the bag to increase the pressure in the tubular member to a level sufficient to cause the flapper valve to expose a mask inhalation port and cover a mask exhalation port whereby the oxygen is passed into the mask for consumption by the subject. Once the contents of the bag have been depleted via squeezing to an extent that the pressure in the body member is insufficient to overcome the bias of the flapper valve, the valve returns to its normal position covering the inhalation port and exposing the exhalation port. At this time, the subject exhales, his expiratory gases passing through the exhalation port, and the bag reinflates. This process is repeated as necessary to facilitate or restore the patients normal breathing pattern.
A functional weakness of this sort of resuscitator is that it is incapable of dispensing pressurized atmospheric air in the event of failure or exhaustion of the pressurized oxygen supply. Specifically, even if the gas source were disconnected from the gas inlet thereby exposing the inlet to the atmosphere, the squeeze bag is not self-restoring. Hence, it cannot create either the negative pressure required to draw air into the inlet or the positive pressure to expel the air therefrom.
U.S. Pat. Nos. 2,399,643, 2,834,339, 3,196,866, 3,316,903, 3,473,529, 4,037,595, 4,077,404, 4,088,131 and 4,121,580 describe self-distending squeeze bag or similar resuscitators variously capable of administering air, oxygen or a mixtures thereof upon compression of the squeeze bag. Pursuant to each of these disclosures, gas flow to and from the subject is effected by the opening and closing of at least one, and usually two or more, spring-biased check valves, flap valves or combinations thereof. In perhaps the simplest of these constructions, i.e., the resuscitators proposed in U.S. Pat. Nos. 3,196,866 and 3,316,903, during expansion of the squeeze bag the oxygen being supplied to the bag will always be mixed with atmospheric air because the resuscitator valve assembly includes ports in communication with the atmosphere and the interior of the bag, which ports are normally open and can only be closed by squeezing the bag. Thus, these resuscitators may together be envisioned as another form of the "oxygen accumulator" type resuscitators previously discussed. And, as noted, resuscitators of this sort are incapable of delivering pure oxygen which may at times be vital depending upon the resuscitation requirements of the subject.
Most of the other resuscitators provided in U.S. Pat. Nos. 2,399,643, 2,834,339, 3,473,529, 4,037,595, 4,077,404, 4,088,131 and 4,121,580 may effectively administer virtually pure oxygen. Nonetheless, their valve assemblies are particularly complex in construction and heavily dependent upon the spring biases of their numerous valves to effect proper resuscitator operation. As such, should the oxygen supply of such a resuscitator be momentarily interrupted, the subject would have to expand considerable inspiratory effort to draw atmospheric air into the resuscitator to satisfy his respiratory requirements. In many instances, the subject may be incapable of such exertion, thereby further aggravating his respiratory distress.
The foregoing demonstrates that pressurized oxygen cannot easily be continuously introduced into a squeeze bag resuscitator without compromising the other functions and essential characteristics of the resuscitator. In efforts to avoid these problems, assorted valving arrangements have been developed for introducing and interrupting the supply of pressurized oxygen into various parts of the resuscitator system. Such valving arrangements are intended to respond automatically to particular conditions or operating states of the resuscitator system, typically function in response to sensings of differential pressures, and are commonly referred to as "demand oxygen supply valves".
Despite their general efficacy, the demand oxygen supply valves heretofore proposed have been unduly complicated in design and operation, costly to manufacture and, because of their numerous parts, susceptible to malfunctioning. One of these valves, that disclosed in U.S. Pat. No. 4,374,521, functions in such manner whereby the pressure of the delivered oxygen impinges upon a flexible flap seal urging the seal into covering relation with ports that communicate with the atmosphere. In the event the flow of oxygen ceases, oxygen pressure is removed from the flap seal and the subject may inspire atmospheric air essentially without resistance. The primary disadvantage of this valve, however, is its sheer complexity. No less than four internal pressure chambers and two biased membrane-type valve elements must work in concert to achieve the desired gas delivery results. Should any of these intricately interrelated components fail to function precisely as designed, oxygen administration will be detrimentally affected, if not totally interrupted.
The assignee of the present invention, Respironics, Inc. of Murrysville, Pa., has developed a simplified squeeze bag resuscitator, discussed at greater length hereinafter, which permits the subject to consume essentially pure oxygen. The oxygen is delivered to a manifold that is in fluid communication with an oxygen reservoir bag, a first flapper valve and a second flapper valve. The first flapper valve regulates gas flow into the squeeze bag and the second flapper valve regulates ambient air flow into the manifold. Under normal operating conditions, the oxygen initially fills the reservoir bag and, if the squeeze bag is in a restoring phase, oxygen flows past the first flapper valve and into the squeeze bag. Alternatively, if the bag is fully restored and the subject inhales, the oxygen may pass the first flapper valve and flow directly to the subject.
Should the oxygen flow be interrupted for any reason, the subject would have ready access to the atmosphere by simply inhaling, thereby drawing the air through the second flapper valve and then the first flapper valve. To assure that ambient air does not mix with the oxygen under normal operation, the spring bias of the second flapper valve has been intentionally designed to be rather significant. Because of this built-in bias, however, the subject may experience considerable resistance when it becomes necessary to breathe air directly from the atmosphere. For reasons mentioned above, the subject may not be able to summon the strength to overcome the bias of the second flapper valve and, consequently, the presence of the resuscitator may hinder rather than promote restoration of his normal respiratory activity.
An advantage exists, therefore, for a squeeze bag type resuscitator including an uncomplicated, substantially bias-free valve means capable of delivering essentially pure oxygen during normal operation while affording a subject unhindered access to atmospheric air in the event of interruption of the oxygen flow.
Apart from the aforementioned deficiencies arising from the construction and/or function of their valve assemblies, optimal performance, versatility and operational convenience of conventional squeeze bag type resuscitator apparatus are encumbered by a number of other component-specific design limitations.
Early forms of resuscitator apparatus commonly included a bellows with a handle at one end thereof, at least one valve for introducing ambient air or other breathing gas into the bellows and a breathing mask at the opposite end of the bellows through which the breathing gas could be pumped into the subject's airway by compressing the bag. To use such an apparatus, an operator would place the breathing mask over the subject's face, grasp the handle and compress and decompress the bellows at appropriate intervals and rates by pushing the handle toward and pulling the handle away from the user's face. Examples of such bellows type resuscitators may be found in U.S. Pat. Nos. Re. 24,193, 2,399,643 and 3,316,903. The structure and function of these apparatus, while generally effective for their intended purposes, nevertheless suffered from several detractions.
First, because the entirety of the resuscitator was positioned directly in front of the subject's face during operation, the apparatus tended to obscure the operator's view of the subject's facial activity which is essential for ascertaining how the subject is responding to the therapy.
Second, the bellows compression force is applied directly toward the subject's face thereby creating percussive effect that is manifestly uncomfortable to the subject. Conversely, by pulling the handle away from the subject's face to expand the bellows, the operator must be cognizant to maintain continued and substantial downward manual force on the mask otherwise the mask will become separated from the subject's face. Obviously, this continuous application of force may also contribute to the subject's discomfort.
The introduction of the squeeze bag style resuscitator (and later versions of bellows type resuscitators) brought forth the notion of connecting the mask to a generally L-shaped tubular member which, in turn, was connected to the squeeze bag or bellows. This seemingly simple but significant development, which is reflected in U.S. Pat. Nos. 3,009,459, 3,262,446, 3,473,529, 4,037,595, 4,077,404, 4,374,521, 4,774,941, 4,821,713, 4,919,132, 5,067,487, 5,109,840 5,140,982 and 5,279,289, effectively alleviated the aforesaid disadvantages of vision obstruction and patient discomfort prevalent in the earlier bellows resuscitators because the bulk of the resuscitator apparatus was disposed laterally away from the subject's face. Even these apparatus, however, were somewhat constrained in application. Specifically, because the L-shaped tubular member is typically a rigid link between the mask and the bellows, the operator must exercise considerable care to assure that the mask does not become separated from the subject's face by shifting of the bellows or squeeze bag. In other words, there is a very limited range of spatial orientations within which the resuscitator may be positioned to productively administer breathing gas.
Greater applicational flexibility was achieved in the squeeze bag resuscitators disclosed in U.S. Pat. Nos. 2,834,339, 3,196,866, 3,291,121 and 4,501,271 which incorporated flexible conduit between the squeeze bag and the subject interface. These constructions thus permit the squeeze bag to be operated in virtually any orientation. However, the use of flexible conduit is not without disadvantages. That is to say, precisely because of its flexibility, such conduit is prone to folding or kinking. Hence, should the conduit become sufficiently occluded during operation, gas flow to the patient may be interrupted.
To overcome the problem of kinking in respiratory gas delivery conduits, U.S. Pat. Nos. 3,858,615, 3,908,704, 4,000,341 and 4,852,564 have proposed the use of kink-resistant flexible hose. Even these hoses, however, possess certain limitations. More particularly, although less susceptible to kinking than standard flexible conduit, hoses of this sort have a minimum bending radius below which even they will begin to kink. Thus, regardless of the respiratory apparatus with which they are used, such hoses must be of sufficient length to assure that the minimum bending radius threshold will not be crossed, even under the most adverse operating conditions. As a consequence, more hose than would otherwise be desirable must be provided to prevent such an occurrence. The aforementioned squeeze bag resuscitator developed by assignee Respironics, Inc. employs such a kink-resistant hose between its squeeze bag and mask. However, the relatively long flexible hose connecting the squeeze bag to the breathing mask renders the resuscitator somewhat more unwieldy than would be desirable in certain situations where space to maneuver the apparatus is limited.
A further advantage exists, therefore, for a short, kink-resistant flexible tubular member for fluidly connecting a squeeze bag, bellows or similar resuscitator component to a breathing mask or similar patient interface means.
In developing the present invention, it was recognized that the versatility of a resuscitator could be enhanced if the junctures of one or more of its primary fluid delivery components could be constructed so as to permit relative rotation between those components.
When designing a leak-free, rotatable fluid seal, one must balance the competing objectives of minimizing rotational torque and maximizing gas leak resistance. As a consequence, improved rotatability typically comes at the expense of decreased leak resistance, and vice versa. It is known, as exemplified by U.S. Pat. Nos. 4,852,563, 4,938,209 and 5,062,420, to provide rotatable seals between various breathing circuit components of respiratory apparatus. In each of these assemblies, however, there exists considerable areas of surface contact between the mating parts. And, since no gaskets or other sealing material is disclosed as being interposed between these parts, the desired sealing effect appears to be created by maintaining a tight friction fit between the parts. Assuming these seals to be leak-free, therefore, the close tolerances between the parts necessarily detrimentally impacts upon their ability to rotate relative to one another. Conversely, if the parts do permit relatively free rotation, then considerable gas leak is unavoidable (again because of the absence of sealing material).
The aforesaid Respironics, Inc. squeeze bag resuscitator includes a generally freely rotatable sealed connection between its flexible hose (discussed above) and a non-rebreathing valve situated between the flexible hose and the breathing mask. This mutually beneficial result was achieved by providing generous part tolerances and a quantity of silicon-based sealing lubricant between the parts. Although beneficial rotation and sealing characteristics are realized using such an approach, the use of silicon material or other conventional lubricants as the sealing/lubricating means adds to the cost of the system and may introduce potentially physically harmful agents into the breathing circuit.
A further advantage exists, therefore, for a resuscitator having a low-torque, low-leak, environmentally-safe swivel seal at the juncture of one or more of its primary fluid delivery components.
In addition to its squeeze bag, the previously discussed Respironics, Inc. resuscitator also includes an oxygen reservoir bag upstream of the squeeze bag which stores a selected volume of pressurized oxygen prior to its introduction into the squeeze bag. The oxygen bag is preferably formed of thin, pliable plastic (e.g., polyethylene film) which, unlike the squeeze bag, is not self-inflating. The oxygen reservoir bag is generally oblate in shape and open at its opposite ends whereat it is taped or otherwise adhesively and sealingly secured to upper and lower manifolds. The manifolds are respectively connected to the non-rebreathing valve and the squeeze bag and are attached to opposite ends of the flexible hose whereby fluid communication is established between the manifolds by virtue of the flexible hose. So constructed, the oxygen reservoir bag establishes a sealed oxygen chamber about the flexible hose and between the manifolds. A disadvantage of this arrangement is that the additional materials (e.g., tape or adhesive) and attendant labor required to adhesively secure the opposite ends of the oxygen reservoir bag to the manifolds undesirably contribute to the manufacturing cost of the resuscitator. Moreover, if care is not taken in the attachment of the oxygen reservoir bag to the manifolds, oxygen may leak from the system.
U.S. Pat. Nos. 4,917,081 and 4,919,132 teach pliable breathing gas storage bags connected at their opposite ends to components of respiratory apparatus. The bag in U.S. Pat. No. 4,917,081 requires supplemental attachment means to assure its sealing connection. The bag in U.S. Pat. No. 4,919,132 merely receives smooth tubular inserts having no structure to which the bag may positively and sealingly engage to prevent gas leakage from the bag.
In connection with a resuscitator of the type having an oxygen reservoir bag, an advantage exists, therefore, for an improved system by which the oxygen reservoir bag may be sealingly attached to the resuscitator without resort to adhesive tape or other superfluous fastening means.
U.S. Pat. No. 4,501,271 exemplifies a conventional, fully disposable resuscitator. Such apparatus is designed for one-time use and effectively prevents cross-contamination. Disadvantageously, however, fully disposable resuscitators must be discarded in their entirety after a single use. Thus, their disposal is expensive and they are costly to maintain as inventory. Further, because many of the resuscitator components are subject to patient contamination, and also because they are not sterilized after usage, resuscitators of this type are not considered to be especially environmentally compatible.
Fully reusable resuscitators, such as that described in U.S. Pat. No. 2,834,339, for example, are sterilizable and capable of multiple usages. While seemingly more economically desirable, these resuscitators require sterilization after each use. As such, considerable handling, disassembly, assembly and testing is needed to assure that the apparatus is not only properly sterilized but that it also functions properly after sterilization. The diseconomies associated with such practice are manifest.
U.S. Pat. Nos. Re. 24,193, 2,834,339, 3,196,866, 3,473,529 and 4,374,521 represent examples of squeeze bag resuscitators whose squeeze bags are self-sealingly or "stretch-fit" onto the remainder of the apparatus. None of these disclosures, however, address the economic, environmental and safety advantages that may be achieved through development of a partially reusable resuscitator, particularly one whose squeeze bag may be repeatedly sterilized and reused and whose other components may be discarded after each use.
A further advantage exists, therefore, for a squeeze bag resuscitator that permits ready sterilization and reuse of its most rugged, costly and yet most easily sterilized component, i.e., its squeeze bag, and which simultaneously affords convenient discardability of its other functional components as an integrated disposable assembly.